Device for removing moisture from a hydraulic medium

ABSTRACT

The device according to the invention for removing moisture from a hydraulic medium ( 2 ) with at least one gaseous drying medium ( 3 ) is characterized in that the drying medium ( 3 ) is air and/or some other working gas with corresponding moisture absorption capability, said drying medium being conducted by means of a delivery device ( 4 ) from an area surrounding the hydraulic medium ( 2 ) to the hydraulic medium ( 2 ) when the moisture content of the respective gaseous drying medium ( 3 ) is lower than the degree of water saturation of the hydraulic medium ( 2 )

The invention relates to a device for removing moisture from a hydraulicmedium with at least one gaseous drying medium.

In hydraulic systems, for example, in the form of large gear units, thehydraulic media, such as lubricants or the like, are exposed to changingenvironmental conditions. The result can be an undesired introduction ofparticles, also in the form of water, into the lubricant, a state thatis basically associated with a degradation of the physical properties,in particular with respect to the targeted lubricating power of suchlubricants. A typical representative of such a problem constitutes thegear units of wind turbines. In order to transform the speed of a rotorof a wind turbine to a speed that is suitable for driving a generator,it is customary to use spur gear systems in the manner of planetary geartrains or systems comprising a pair of gear rings. The rotor consistingof a hub with two or more blades has for the gear unit a drive with ahigh torque at a well-known very low speed. The gear unit in turn hasfor the generator a drive with a lower torque at, for example, a speedtransformation of 80-fold.

For this reason, for more than 20 years it has been the practice to use,for example, planetary gear units, which are comparatively compact withrespect to the installation requirement. Such speed transforming gearsare in many respects units with components that are exposed to stress,so that the wear of such units has to be minimized, because themaintenance, repair, and replacement of the key wear components of suchgear units is often time consuming and cost intensive.

Since some of the components of such gear units stand as high as a man,they can be greased at the respective gearwheels and bearing locationseither by oil recirculating lubrication systems with continuoustransport and application of lubricant by means of gear oil pumps from agear oil sump or by splash lubricating systems. In the case of splashlubricating systems, the gearwheels of the gear unit are partiallyimmersed in immersion baths with a supply of lubricant.

Gear units, which are characterized in particular by a large volume orby large inner surfaces of the gear housing, tend to collectcondensation water in their interior. This process is facilitated,especially in the case of iteratively operating gear units, by theirepisodically heating up and then subsequently cooling down.

Gear units of wind turbines are exposed, as a function of theirinstallation site, more or less to cyclical operating and rest periodsdue to the fluctuation in the strength of the wind. In addition, eventhough these gear units are housed in system housings, for example, on atower of a wind turbine, they are exposed more to the changing weatherconditions, in particular the moist air, than is the case with othergear units, which are arranged stationarily in a defined environment.The result is that the water content in the lubricant of such gear unitscan increase. Water has an adverse effect on the physical properties oflubricants, such as gear oil, and can contribute to the premature agingof the lubricating oil, a feature that in turn has a damaging effect onthe components of the gear unit.

In order to decrease the atmospheric moisture content in a gear housingand at the same time also the water content in the lubricating oil, itis known, for example, from DE 100 31 004 B4 to use a container withaluminum oxide that contains an absorptive agent for the humidity in theair. In the solution known from the prior art, the routing of the airflow is selected in such a way that this air flows through theabsorptive agent. Check valves are used for the purpose of allowing theabsorptive agent to flow through the container only when the air isdelivered, but not when the air is removed. This arrangement preventsthe oil laden air from flowing, for example, out of a gear sump, overwhich the dried air from the container sweeps.

In principle, it is also known from EP 0 135006 A2 to configure a devicefor aerating with dried air in such a way that a chemically activedesiccant is used, through which air flow can take place. As a result,the moisture is removed from this air. These prior art devices aresuited for continuous operation with long maintenance intervals, whichis the customary operating mode of a wind power system, only undercertain conditions. In addition, the volumetric flow rate of the driedair that is provided by such devices is limited.

EP 1 736 665 A2 discloses a method for removing the moisture inside thetower of a wind turbine. The prior art wind turbine comprises aninterior, which is sealed off at least substantially against an airexchange, and a moisture extraction device, which is connected to theinterior by means of an inlet for moist air and an outlet for dry airand is disposed between said moist air inlet and said dry air outlet.The moisture extraction unit known from the prior art draws off themoist air from the interior of the wind turbine, extracts water from themoist air, and returns the dried air back into the interior as a closedloop. A negative pressure area can be generated at the moist air inletby sucking in the moist air from the interior; and, correspondingly, anarea exhibiting excess pressure can be generated at the dry air outletby expelling the dried air into the interior, so that a drying airstream is formed in the interior between the negative pressure area andthe excess pressure area. The moisture extraction device extracts themoisture from the air from the interior and can comprise a heating unit.

Based on the aforementioned prior art, the object of the presentinvention is to provide a device for removing moisture from a hydraulicmedium with at least one gaseous drying medium; and this device iscapable of permanently minimizing the moisture content of a hydraulicmedium in a simple way.

This object is achieved with a device for removing moisture from ahydraulic medium having the features specified in claim 1 in itsentirety.

The inventive device for removing moisture from a hydraulic mediumpreferably uses air from the surrounding area of a hydraulic medium asthe drying medium for drying the hydraulic medium, preferably withoutinterpositioning of chemically active moisture absorbing agents. The airfrom the surrounding area of the hydraulic medium is delivered by thedevice to the hydraulic medium only if the air has a lower atmosphericmoisture content than the air in the gear housing, for example, a lowermoisture content than the degree of water saturation of the hydraulicmedium that is converted to the temperature of the ambient air.

Especially in the case of gear housings having a large volume andcorrespondingly large surface areas on which the condensate can beformed, it is necessary to have large volumetric flow rates of air inorder to dry the hydraulic medium, which is present as the lubricant, ina lubricant sump. In particular, the air or air that surrounds thehydraulic medium outside the gear unit and that is not conducted over achemical absorbent lends itself especially well for this purpose,because this ambient air is available in unlimited quantities at nocost. The device delivers, based on its design configuration, an airstream into the gear housing or to the hydraulic medium only if themoisture content of the air is lower than the degree of water saturationof the lubricant that is converted or adapted to the temperature of theair, so that when the ambient air flows over the lubricant or thehydraulic medium, this ambient air is capable of extracting an adequateamount of water from said lubricant, in order to “dry” the lubricant inthis way.

The device preferably comprises a sensor system, which is capable ofdetermining the moisture content and the temperature of the ambient airas well as the moisture content and the temperature of the hydraulicmedium. At the same time, inductive, capacitive, or other measurementmethods may be used. A control and/or regulating unit of the devicetakes, as a function of the measured physical parameters, the air fromthe surrounding area and conveys this air to the respective hydraulicmedium, which is stored preferably in the interior of a gear housing,when the air has a lower moisture content than the hydraulic mediumitself or a quantity of the air supply that may be present above thehydraulic medium in the gear housing.

The control and/or regulating unit of the device for removing moisturefrom a hydraulic medium preferably actuates a fan, which is put intooperation as soon as the control and/or regulating unit detects a dryingpotential for the air in the surrounding area of the hydraulic medium.Moreover, the fan can be shut off; that is, an intermittent dryingoperation is provided for the hydraulic medium. The drying medium, i.e.,air, can be produced, instead of through a fan, through diverting of asuitably strong air flow from the surrounding area of the hydraulicmedium or the gear housing, such as from the surrounding area of a windturbine tower or an associated system housing. Especially suitable forthis purpose are, for example, inlet channels having an outer end, onwhich there is an inlet scoop that is configured as a hood, in order tobe able to withdraw air from the surrounding area with almost nopressure loss. Then the ambient air flows at a slight pressure loss, forexample, into the gear housing of the wind turbine in order to dry thelubricating oil, which may be found in said gear housing, by means of aturbulent flow over said lubricating oil, a feature that is especiallyenergy efficient.

Prior to conveying to the hydraulic medium, the air, or morespecifically the drying medium, can additionally be conducted over aheating unit, where the heating element releases the air, or morespecifically the drying medium, from the residual moisture, anarrangement that can significantly raise the possible absorptioncoefficient of water.

In order to achieve a suitably long retention time, the inlet openingfor the drying medium on the gear housing is preferably set as far apartas possible from an outlet opening for the drying medium out of the gearhousing. In addition, it may be advantageous to provide a drying filterfor the drying medium upstream of the outlet opening.

The result of these proposed design measures is that the flow path ofthe air inside the interior of the gear housing is as long as possible,so that the retention time of the air or the drying medium in the gearhousing can be increased to the maximum amount. This arrangement ensuresthat it is possible for the air to make spatial contact with thelubricant for a period of time that is as long as possible, in order todry the lubricant in the gear housing. Furthermore, this arrangementensures a good water exchange between the lubricant and the ambient airor some other drying medium that is used and that can also be mixed withthe air.

In an especially preferred embodiment, the outlet opening for the air,laden with moisture, is arranged in the vicinity of one or more bearinglocations for the movable components in the gear housing. It can also beadvantageous to provide a bearing nest or a bearing itself for themovable parts or shafts in the gear housing with an outlet opening. Thisarrangement also allows a plurality of outlet openings, with the resultthat impurities cannot enter in the bearings. Such an introduction ofimpurities is prevented by the excess pressure in the gear housing,because only the drying medium can flow from the interior of the gearhousing past the bearings to the exterior of the gear housing.

If the hydraulic medium to be dried is part of a gear unit in a windturbine, then it may be advantageous to convey the air or drying mediumthrough a system housing comprising such units as transformers and powercomponents, such as frequency converters and switching systems, in orderto heat up and remove the moisture from the air or the drying medium. Inthis case, the air can also be used as a coolant for the said modules.

In addition to the aforementioned ambient air as the drying medium, itis also possible to use some other working gas having a suitablemoisture absorbing capacity. In this case, the air can also be presentas a mixture with such a working gas. In an additional embodiment of theinvention, the gaseous drying medium can also be provided additionallywith moisture absorbing microparticles which absorb the correspondingmoisture and then would also be removable again from the gaseous dryingmedium stream by means of a filter device. Thus, the said particles canbe processed again in a closed loop, in particular by removing themoisture by drying and then subsequently feeding again into the gasdrying medium stream. In this respect, the closed loop can also be runwith the respective drying medium without the infeed of particles.

The invention is explained in detail below by means of one exemplaryembodiment that is depicted in the drawing.

The single FIGURE is a longitudinal view in schematic form of a gearunit of a wind turbine with a circuit diagram of a system for feedingambient air into a gear housing of the gear unit.

The FIGURE shows in schematic form, not drawn to scale, a partiallongitudinal view of a device 1. This device is configured for removingmoisture from a hydraulic medium 2 in a gear housing 9 of a windturbine. A gear unit 15 of this type is used in so-called wind turbines,in which a rotor, which can be driven by wind power (not illustrated)delivers its driving power to an input shaft 16. Upon passing throughthe gear unit 15, the driving power is delivered to an output shaft 17,to which, for example, a generator for generating electric power can beconnected. The rotor of such a wind turbine has very low speeds andtypically a high torque. Since a generator for generating electric powerneeds higher input speeds, the gear unit generally provides a speedincrease ratio of, for example, 1:80. Types of gears, such as aplanetary gear train or other spur gear systems with oblique or straightteeth, are also used in such wind turbines.

In the exemplary embodiment shown in the present embodiment, the gearunit 15 is designed as a spur gear system comprising a plurality of gearstages 18, of which only the components or shaft ends are shown to someextent. In particular, it is also possible to use gear units having twogear stages, of which the first gear stage is a planetary gear train andthe second gear stage is preferably a spur gear system. The gear stagesare surrounded by a gear housing 9 that is configured in the shape of acylinder or a box.

In the illustrated exemplary embodiment, the gear stages 18 arelubricated by a splash lubricating system. For this purpose, there is asupply of lubricant 10 in the form of a gear oil. In an immersion bath,which is formed in this way, the gearwheels (not illustrated) of thegear stages 18 are at least partially immersed, so that all of theengaged tooth flanks and also the face sides of the gearwheels areconstantly coated with an oil.

Such gear units have a volume inside their gear housing that is notinsignificant. The volume of air that is present in the gear housing 9and that may be found over the lubricant 10 is exposed to temperaturefluctuations that are induced, on the one hand, by the outsidetemperatures that change as a function of the weather and, on the otherhand, by the non-uniform operation of such wind turbines due to anincrease in temperature caused by friction and material expansion andthe cooling down phases with respect to the gear unit. As a result,condensate forms on the walls of such a gear housing 9, because thesewalls are often good heat conductors. The descending water flows into alubricant sump and degrades the quality of the lubricant or the oil and,in so doing, shortens the oil or lubricant change intervals. Inaddition, it may lead to corrosion in the interior of the gear housing9; and the oil aging of the lubricant can in turn cause damage to thegear unit itself.

In order to eliminate the cause for water entering into the lubricant10, the invention provides, on the one hand, to eliminate the moist airthat is present in the gear housing 9 and, on the other hand, to providethat the dry air is conducted into the gear housing 9. For this purpose,a device, which is designated as a whole as 1, is provided for removingmoisture from a hydraulic medium 2. In this case, the device 1 ensuresthat ambient air is delivered into the gear housing 9 as drying medium 3only if this air has a lower moisture content than the degree of watersaturation of the lubricant 10 at comparable temperatures. If the gearunit heats up, it is most likely that water vapor will be permanentlydischarged from the lubricating oil into the surrounding area, locatedabove said lubricating oil, inside the gear housing 9, and which is tobe removed from there, as described above.

In the exemplary embodiment depicted in the figure, the device forsupplying the ambient air or for forming an ambient air stream into theinterior of the gear housing 9 comprises a conveying device 4 in theform of an axial fan, which is driven by an electric motor 19 and sucksthe ambient air into the gear housing 9 and then blows said air into theinterior of the gear housing 9 by means of a filter 20, which isconnected upstream of an input opening 8 on the gear housing 9. The fanruns only if the matching of sensor signals of a sensor 5 fordetermining the moisture content and the temperature of the dryingmedium 3 (ambient air) and a sensor 6 for determining the moisturecontent and the temperature of the lubricant 10 in a control and/orregulating unit 21 shows that the ambient air is capable of absorbingthe water in the gear housing 9 and of removing said water from the gearhousing 9 through an outlet opening 11 or a plurality of outlet openings11′.

There are, as illustrated, a plurality of outlet openings 11′ on thegear housing 9; and these outlet openings are arranged at the bearinglocations 13 for the shafts 14 in an outer wall of the gear unit 9.

It is also possible for the ambient air, which has absorbed the water,to flow through the roller bearings of the shafts 14 directly from theinside to the outside. In order for the roller bearings to be traversedby flow, these roller bearings can exhibit in part passage points (notillustrated) for the air steam in the area of the bearing cages. Inaddition, it is ensured that the air laden with impurities cannot flowinto the area of the bearing locations 13, because an excess pressuresystem from the inside to the outside is created relative to theinterior of the gear housing 9. Since the ambient air is provided withwater, suitable corrosion protection measures for the bearing locationsof the shaft have been provided, however, as a general rule.

To the extent that the bearing locations 13 will not be used as theoutlet opening 11′, there is also the possibility of providing adelivery point at an outlet opening 11 on the gear housing 9, where thisoutlet opening is located as far away as possible from the inlet opening8. This delivery point can be arranged downstream of the drying filter12. The drying filter 12 preferably has a water absorbing material bedor the like and is traversed by flow from the outside to the interior ofthe gear housing 9 when the gear unit 15 is not running and, as aresult, the air in the gear housing 9 is cooling down, because, in sucha case, the air in the interior of the gear housing 9 can contract asrequired. There is, however, also the possibility of providing a vacuumsuction device (not illustrated) in the flow direction of the dryingfilter 12, downstream of said drying filter. This vacuum suction devicecan transport in a sucking manner the interior of the gear housing 9, ormore precisely the ambient air that is laden with moisture, out of thegear housing. In the event of a backflow, which can also be suppressed,if desired, by means of a valve assembly, which is not shown in detail,the air, flowing back through the outlet opening 11, would be dried atthe drying filter 12 in any event before entering into the gear housing9.

It is also possible to arrange a heating unit 7 in the influent flowpath of the ambient air stream to the gear housing 9. In this case, thewaste heat from the power components of the wind turbine can be used forheating in order to suitably reduce the moisture in the air flowing inthe gear housing 9. As an alternative or in addition to the heating unit7, it is also possible to use, as a function of the environmentalconditions, a cooling device (not illustrated), which preferablyperforms a cooling function up to below the dew point (dehumidifier).

Instead of the ambient air, it is also possible to use some otherworking gas having a suitable moisture absorbing capacity as the dryingmedium. Furthermore, it is possible to mix the ambient air with someother working gas. Moreover, it can be provided that a particle contentis introduced into the gaseous drying medium and that this particlecontent lends itself especially well to absorbing moisture. As analternative or in addition to the drying filter 12, a filter forseparating the particles from the gaseous drying medium stream couldthen be provided.

1. A device for removing moisture from a hydraulic medium (2) with atleast one gaseous drying medium (3), characterized in that the dryingmedium (3) is air and/or some other working gas having a correspondingmoisture absorbing capacity; and that said drying medium is conducted bymeans of a conveying device (4) from an area surrounding the hydraulicmedium (2) to the hydraulic medium (2) when the moisture content of therespective gaseous drying medium (3) is lower than the degree of watersaturation of the hydraulic medium (2).
 2. The device according to claim1, characterized in that the device (1) comprises at least one sensor(5) for determining the moisture content and the temperature of thedrying medium (3), conveyed to the hydraulic medium (2), and/or a sensor(6) for determining the moisture content and the temperature of thehydraulic medium (2).
 3. The device according to claim 1, characterizedin that the conveying device (4) can be actuated, as a function of thesignals of the sensors (5, 6), by means of a control and regulating unit(21).
 4. The device according to claim 1, characterized in that thedrying medium (3) is conducted over a heating unit (7).
 5. The deviceaccording to claim 1, characterized in that the conveying device (4)conveys the drying medium (3) through an inlet opening (8) to thehydraulic medium (2) that is located in a housing, in particular, in agear housing (9).
 6. The device according to claim 1, characterized inthat the hydraulic medium (2) is a lubricant (10), which is preferablyreceived in a gear housing (9).
 7. The device according to claim 1,characterized in that the conveying device (4) is a discharging devicefor discharging the moving drying medium from the area surrounding thehydraulic medium (2).
 8. The device according to claim 1, characterizedin that the drying medium (3) issues from the gear housing (9) at leastat one outlet opening (11, 11′) that is located at a distance from theinlet opening (8) on the gear housing (9).
 9. The device according toclaim 1, characterized in that a drying filter (12) for the dryingmedium (3) is arranged upstream of the outlet opening (11).
 10. Thedevice according to claim 1, characterized in that the outlet opening(11′) is arranged on a bearing location (13) or bearing nest for a shaft(14) on the gear housing (9).
 11. The device according to claim 1,characterized in that the outlet opening (11′) is arranged around abearing location (13) or bearing nest for a shaft (14) on the gearhousing (9).
 12. The device according to claim 1, characterized in thatthe gear housing (9) is part of a wind turbine.
 13. The device accordingto claim 1, characterized in that this device is part of a systemhousing or a tower of a wind turbine, and is a heating unit (7) for thedrying medium (3) by means of units, such as transformers, frequencyconverters, or a switching system of a unit module of the wind planthaving waste heat that is used for heating the drying medium (3).